Many modern systems include air or liquid filters to ensure proper or reliable performance. For example, automobiles include air and fuel filters to remove dirt and other particulates from the air and fuel that are mixed and then ignited within their internal combustion engines. As a consequence of their proper operation, these filters collect particulates over time and increasingly restrict the flow of air or fuel into engines. Eventually, the filters become more restrictive than desirable and require replacement.
To facilitate timely filter replacement, automobiles and other systems sometimes include filter-monitoring devices, which monitor pressure or vacuum levels that result from fluid flow through associated filters. These devices are calibrated to detect when particular pressure or vacuum conditions occur and to respond to such occurrences in particular ways. For example, some devices, referred to herein as filter-monitoring switches, open or close an electrical switch, which is typically wired to illuminate a warning light or to send a signal to an engine computer for further processing.
The present inventors have recognized that commercially available filter-monitoring switches suffer from at least three problems. First, some filter-monitoring switches are overly sensitive to spiking or fluttering pressures and thus prematurely signal filter replacement or provide a fluttering output signal that is difficult to process. Second, overly sensitive switches experience recurrent arcing between their electrical contacts that degrades performance, and often leads to premature failure of the switches. And, third, some switches allow dust and water intrusion that can also degrade performance and cause failures.
Accordingly, the present inventors have recognized a need to improve conventional filter-monitoring switches.